1. Field of the Invention
The invention relates to a cooking oven to be cleaned through pyrolysis having a catalyst in the smoke evacuation circuit.
2. Summary of the Prior Art
Pyrolysis is a known operation for cleaning ovens that involves destroying, by heat, the grease deposits or stains that appear on the walls of an oven during cooking or reheating foods. The temperature of the oven must be 500.degree. C. in order for the pyrolysis to be normally performed. This temperature is obtained by simultaneously operating at least the vault resistances and the sole resistances that are included in the oven.
However, the burning of greases or stains generates smoke which contains more or less harmful gases such as carbon monoxide or carbon dioxide. The gas content is higher when burning is incomplete.
The smoke generated by the burning of the greases is exhausted into the rooms where the oven is installed. It is thus necessary that the toxic gases be neutralized or oxidized when they escape from the oven so that their presence does not jeopardize the atmosphere of the room.
In order to perform this operation, it is known to dispose a palladium based oxide in the smoke evacuation circuit. However, this type of catalyst begins to operate, i.e. becomes effective, when it reaches a temperature of about 350.degree. C. When the smoke evacuation pipe in which the catalyst is placed reaches 350.degree. C., the oven has a considerably higher temperature, at which time the inner atmosphere is saturated by the smoke fumes.
In order to render the catalyst effective prior to the oven reaching such a saturation temperature, it is known to dispose a resistance for heating the catalyst, adjacent to the catalyst, in the smoke evacuation pipe.
Therefore, the catalyst is brought to a temperature of 350.degree. C. and becomes effective before the temperature of the oven reaching the saturation temperature.
However, this structure presents certain drawbacks. During cooking, deposits of grease or stains also appear on the catalyst heating resistance. This resistance does not have sufficient power to reach a temperature high enough for these deposits to be destroyed. This means that their presence reduces the electric resistance of the filament, thus provoking an abnormal increase of the current flowing through it and of its temperature, and thus reducing its lifespan.
It is necessary to replace the catalyst heating resistance when its resistance is out of range. This operation is made difficult by the lack of accessibility of the catalyst heating resistance.
In order to overcome this drawback, ovens cleaned by pyrolysis are known in which the catalyst heating resistance does not come into contact with fumes.
However, the production of such devices is difficult since it is necessary to provide a special housing for the catalyst heating resistance in the smoke evacuation pipe.